Computer-generated animation generally involves specifying objects, their behavior, lighting, etc., and submitting data representing animator selections to an animation system that reads that data and performs the necessary calculations to determine how objects in a virtual or simulated environment would behave, move, look, etc. The animation result is then often rendered for display on a 2D or 3D display. In modern animation, the demands for visual expression prevent an animator from manually specifying the specific details of each pixel in each frame of animation. Instead, the animator specifies objects, lighting, effects, and their characteristics and the animation system computes frames of animation images that might represent what the animator specified.
Movement of an object could be specified point-by-point, frame-by-frame, but that is tedious and can be nearly impossible to be made to look like “natural” movement. Instead, with modern animation, an animator specifies inputs or constraints, such as the (x, y, z, t) coordinates of an elbow, leg, bone, anchor point, etc. for a collection of object points at a collection of times, and a kinematics engine would specify positions of those objects in each frame, applying those constraints. In some cases, there may be too many points to effectively manually specify each of the points, such as where the animation involves hair or cloth or other flowing objects.
Realistic animation based on force field effects is important for rendering realistic animated images. Directional winds are the most commonly used force field models for animating believable hair motion. While prior models produce a nice sense of where the wind is coming from, they can't capture some important phenomenon, such as how each hair occludes the wind (i.e., the wind intensity) when the wind traverses a mass of hairs or objects around it.
In some cases, hair is an important feature or extension of a character. Creating animation for hair that possesses its own dramatic and expressive personality but still appears realistic and physically convincing can pose a challenge. Hairs could be individually placed, but that can be an intractable task in many cases.
Previous models include using a shaper (e.g., a simple geometric shape) such as a sphere to simulate a head of an animated figure. In such models, the attenuation factor for a given point is based on the distance from the center of the sphere. This type of model, however, is less accurate and requires more manual configurations.
In other models, force fields (e.g., wind) are treated as a constant everywhere portions of an object (e.g., hair, string, cloth) are present. This may result, however, in inaccurate modeling of force field effects.
Accordingly, what is desired are improved methods and apparatuses for solving some of the problems discussed above with respect to rendering realistic animated images, while reducing at least the drawbacks described above.